Combination insulator and organic semiconductor formed from self-assembling block co-polymers

ABSTRACT

A semiconductor structure including an insulator layer formed of a first polymer. The structure also includes an organic semiconductor layer formed of a second polymer. The polymers self-assemble into a well-ordered co-polymer structure with the semiconductor layer positioned adjacent the insulator layer. The structure may be an organic, thin-film semiconductor device including, without limitation, a transistor, a multi-gate transistor, a thyristor, and the like. Also disclosed is a process of manufacturing the semiconductor structure.

This application is a divisional of U.S. patent application Ser. No.10/810,525 filed Mar. 26, 2004 now U.S. Pat. No. 6,930,322, the entiredisclosure of which is expressly incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to organic semiconductors and,more particularly, to a combination insulator and organic semiconductorformed from self-assembling block co-polymers. Most particularly, thepresent invention relates to an organic, thin-film transistor.

BACKGROUND OF THE INVENTION

There are two major types of field effect transistors or FET's: themetal-oxide-semiconductor field effect transistor or MOSFET (also calledan insulated-gate FET, or IGFET), and the junction-gate FET, or JFET. AnFET has a control gate and source and drain regions formed in asubstrate. The control gate is formed above a dielectric insulator thatis deposited over the area between the source and drain regions. Asvoltage is applied to the control gate, mobile charged particles in thesubstrate form a conduction channel in the region between the source anddrain regions. Once the channel forms, the transistor turns “on” andcurrent may flow between the source and drain regions.

FIGS. 1 and 2 illustrate the structures of two main types ofconventional thin-film transistors. As illustrated in FIG. 1, one typeis a bottom contact structure 10. Structure 10 has a control gateelectrode 6 formed above a dielectric insulator 1. Insulator 1 is formedover a semiconductor 2. In turn, semiconductor 2 is formed over asubstrate 3. A source electrode 4 and a drain electrode 5 are formed insubstrate 3. Gate electrode 6 is deposited over the area between sourceelectrode 4 and drain electrode 5.

As illustrated in FIG. 2, a second type of conventional transistor is atop contact structure 20. Structure 20 has a control gate electrode 6formed in or on the substrate 3. Insulator 1 is formed over substrate 3and gate electrode 6. In turn, semiconductor 2 is formed over insulator1. A source electrode 4 and a drain electrode 5 are formed on top ofsemiconductor 2. Gate electrode 6 is formed under the area betweensource electrode 4 and drain electrode 5.

Transistors are used as either amplifying or switching devices inelectronic circuits. In the first application, the transistor functionsto amplify small ac signals. In the second application, a small currentis used to switch the transistor between an “on” state and an “off”state.

The bipolar transistor is an electronic device with two p-n junctions inclose proximity. The bipolar transistor has three device regions: anemitter, a collector, and base disposed between the emitter and thecollector. Ideally, the two p-n junctions (the emitter-base andcollector-base junctions) are in a single layer of semiconductormaterial separated by a specific distance. Modulation of the currentflow in one p-n junction by changing the bias of the nearby junction iscalled “bipolar-transistor action.”

External leads can be attached to each of the three regions and externalvoltages and currents can be applied to the device using these leads. Ifthe emitter and collector are doped n-type and the base is doped p-type,the device is an “npn” transistor. Alternatively, if the opposite dopingconfiguration is used, the device is a “pnp” transistor. Because themobility of minority carriers (i.e., electrons) in the base region ofnpn transistors is higher than that of holes in the base of pnptransistors, higher-frequency operation and higher-speed performancescan be obtained with npn devices. Therefore, npn transistors comprisethe majority of bipolar transistors used to build integrated circuits.

An insulated-gate bipolar transistor or “IGBT” is used to control theflow of electric power. It contains four regions of semiconductormaterial of alternate conductivity type, and it has three externalterminals. The device controls the flow of power in response to a signalapplied to one of its terminals, called the gate. The presence of anappropriate gate signal turns the device on and allows electric currentto flow through it; removing the gate signal turns the device off,blocking the flow of current.

A “thyristor” is a semiconductor device similar to an IGBT. Like anIGBT, a thyristor contains four regions of semiconductor material ofalternate conductivity type and has three external terminals, one ofwhich is the gate. As in the IGBT, applying an appropriate gate signalturns the thyristor on, allowing the flow of electric current throughit. Unlike an IGBT, however, removing the gate signal from a thyristordoes not shut off the flow of electric current through the device. Oncea thyristor turns on in response to the application of a gate signal, itcannot be turned off simply by removing the gate signal. The thyristorthus exhibits “latching” behavior. In response to the application of anappropriate gate signal, the device turns on and remains on even if thegate control signal is removed. Turning a thyristor off typicallyrequires reduction of the current flowing through the device below athreshold level.

The latching property of the thyristor arises from the structure of thedevice. The four alternating semiconductor regions in a thyristorinherently incorporate two three-layer combinations, each of which has aforward current gain, denoted as σ₁ and σ₂, respectively. It is wellknown that a thyristor will not latch if the sum of σ₂ and σ₂ is lessthan one.

A MOSFET is also a three-terminal device that is used to control theflow of electric power. Unlike IGBT's and thyristors, however, MOSFETshave only three semiconductor regions. A MOSFET controls the flow ofpower through the device in response to an appropriate control signalapplied to its gate terminal. MOSFETs are similar to IGBTs in that theycan be used to control the flow of electric power by selectivelyapplying and removing an appropriate gate signal. MOSFETs do not exhibitthe “latching” behavior of thyristors, but thyristors can typicallycarry larger amounts of electric power.

IGBTs combine the controllability of a MOSFET with thehigh-power-carrying capabilities of a thyristor. Because theyincorporate a four-layer structure similar to a thyristor, however,IGBTs incorporate two three-layer combinations of regions of alternateconductivity and therefore exhibit latching if subjected to certainelectrical conditions, such as high voltages.

The semiconductor-based devices and systems described aboveconventionally incorporate inorganic semiconductor materials, forexample, silicon-based materials. Organic semiconductors have thepotential to replace conventional inorganic semiconductors in a numberof applications, and further may provide additional applications towhich inorganic semiconductors have not been utilized. Such applicationsmay include, for example, display systems, mobile devices, sensorsystems, computing devices, signal reception devices, signaltransmission devices, and memory devices.

Replacement in these applications is anticipated because organicsemiconductors have advantages when compared to conventionalsemiconductors. One important advantage is the relative ease ofprocessing organic semiconductors. Another advantage is the improvementin electrical properties possible using organic semiconductors. Theelectrical properties of organic semiconductors depend largely on theirintrinsic material properties, morphology, crystallinity, and thepacking density of molecules.

More specifically, for organic thin-film transistors, the interfacesbetween components have played an important role. The interface betweenthe gate insulator and the organic semiconductor determines transistorstability: the cleaner the interface, the more stable is the thin-filmtransistor. Currently, the organic semiconductor and the insulatorlayers are deposited separately by using vacuum deposition, spincoating, ink-jet printing, and the like. Therefore, the chances ofcontamination and imperfection at the interface are high, renderingcurrent processes unlikely to generate a high yield of reliable devices.

In addition, the structure of the transistor plays another importantrole in defining the electrical properties of the device. Conventionaltransistor structures have a gate consisting of a gate insulator and agate electrode located on only one side of the semiconductor. Thisrestricts transistor properties.

The semiconductor industry has recently begun to recognize theimportance of multi-gate semiconductor structures—although usingconventional silicon-based materials. See, e.g., M. Masahara and E.Suzuki, “AIST Announces World's Thinnest Vertical-Type Double-GateMOSFET Using Newly Discovered Process,” AIST Today Int'l Ed. No. 8,pages 10–12 (2003) (incorporated in this document by reference). Themulti-gate structure has more than one gate around the semiconductor.The structure allows optimal control of transistor properties,especially of the threshold voltage, and both minimizes powerconsumption and reduces switching error. More specifically, less draincurrent is required to turn on the device and, therefore, less power isconsumed while the device is operating. In addition, each of themultiple gates can be used to control the gate threshold voltage ofanother gate, which allows optimal control of the threshold voltage.

The vertical-type, double-gate MOSFET considered by authors M. Masaharaand E. Suzuki is designed to eliminate the short-channel effect, whichis the mutual interference between the source and the drain as thedistance between those components is reduced through miniaturization, bylayering a thin channel between the two gates. As the authors recognize,however, fabrication of multi-gate structures has proven difficult. Theauthors disclose fabrication of the world's thinnest channel (about 15nm thick) by using a conventional complementarymetal-oxide-semiconductor (CMOS) production process in combination witha newly discovered process in which the etching rate of an alkalinesolution is retarded at the surface exposed to ion bombardment.

To overcome the shortcomings of conventional semiconductor devices andmanufacturing processes, a new device and process of manufacture areprovided. An object of the present invention is to provide an improvedcombination insulator and organic semiconductor. A related object is toreduce the possibility of an imperfect or contaminated interface betweenthe insulator and the organic semiconductor. Another object is to reducethe number of steps during the process of manufacturing a combinationinsulator and organic semiconductor.

It is still another object of the present invention to provide anorganic, thin-film transistor having improved electrical properties. Arelated object is to provide an organic, multi-gate, thin-filmtransistor. More specific objects are to allow optimal control oftransistor properties, especially of the threshold voltage, and to bothminimize power consumption and reduce switching error. Yet anotherobject is to provide a process facilitating the manufacture ofmulti-gate transistor structures.

SUMMARY OF THE INVENTION

To achieve these and other objects, and in view of its purposes, thepresent invention provides a semiconductor structure including aninsulator layer formed of a first polymer. The structure also includesan organic semiconductor layer formed of a second polymer. The twopolymers self-assemble into a well-ordered co-polymer structure with thesemiconductor layer positioned adjacent the insulator layer. Thestructure may be an organic, thin-film semiconductor device including,without limitation, a transistor, a multi-gate transistor, a thyristor,and the like.

The present invention also provides a process of manufacturing athin-film organic semiconductor device. The process includes, as a firststep, providing a substrate. Next, an insulator layer formed of a firstpolymer and an organic semiconductor layer formed of a second polymerare applied to the substrate; the polymers self-assemble into awell-ordered co-polymer structure with the semiconductor layerpositioned adjacent the insulator layer. Then parts of the insulator areremoved between the organic semiconductor layer, thereby separating thelayers of organic semiconductor.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, but are notrestrictive, of the invention.

BRIEF DESCRIPTION OF THE DRAWING

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawing. It is emphasizedthat, according to common practice, the various features of the drawingare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawing are the following figures:

FIG. 1 illustrates a conventional bottom contact transistor structure incross-section;

FIG. 2 illustrates a conventional top contact transistor structure incross-section;

FIG. 3A is a cross-sectional view of a co-polymer lamella structurehaving an insulator and an organic semiconductor layered in parallel, orhorizontally oriented, with the insulator on the top and the organicsemiconductor on the bottom according to the present invention;

FIG. 3B is a top view of the lamella structure shown in FIG. 3A;

FIG. 4A is a cross-sectional view of a co-polymer cylinder structurehaving an insulator and an organic semiconductor layered in parallel, orhorizontally oriented, with cylindrical structures of organicsemiconductor surrounded in a matrix of insulator, according to thepresent invention;

FIG. 4B is a top view of the parallel cylinder structure shown in FIG.4A;

FIG. 5A is a cross-sectional view of a co-polymer cylinder structurehaving an insulator and an organic semiconductor vertically layered,with cylindrical structures of organic semiconductor surrounded in amatrix of insulator, according to the present invention;

FIG. 5B is a top view of the vertical cylinder structure shown in FIG.5A;

FIG. 6A is a cross-sectional view of a co-polymer lamella structurehaving an insulator and an organic semiconductor vertically layered,with alternating lamellae of the insulator and the organicsemiconductor, according to the present invention;

FIG. 6B is a top view of the vertical lamella structure shown in FIG.6A;

FIG. 7A is a cross-sectional view of a single-gate transistor structureformed according to the present invention;

FIG. 7B is a side view of the single-gate transistor structure shown inFIG. 7A;

FIG. 8A is a cross-sectional view of a dual-gate transistor structureformed according to the present invention;

FIG. 8B is a side view of the dual-gate transistor structure shown inFIG. 8A;

FIG. 9A is a cross-sectional view of a tri-gate transistor structureformed according to the present invention;

FIG. 9B is a side view of the tri-gate transistor structure shown inFIG. 9A;

FIGS. 10A, 10B, 10C, 10D, and 10E illustrate in cross-section thevarious structures formed during the steps of the process used toincorporate the parallel cylinder structure shown in FIGS. 4A and 4Binto a multi-gate thin-film transistor structure according to thepresent invention;

FIGS. 11A, 11B, 11C, 11D, and 11E illustrate in cross-section thevarious structures formed during the steps of the process used toincorporate the vertical cylinder structure shown in FIGS. 5A and 5Binto a multi-gate thin-film transistor structure according to thepresent invention;

FIG. 11F is a top view of the structure shown in FIG. 11E;

FIGS. 12A, 12B, 12C, 12D, and 12E illustrate in cross-section thevarious structures formed during the steps of the process used toincorporate the vertical lamella structure shown in FIGS. 6A and 6B intoa multi-gate thin-film transistor structure according to the presentinvention; and

FIG. 12F is a top view of the structure shown in FIG. 12E.

DETAILED DESCRIPTION OF THE INVENTION

As used in this document, a polymer is a non-metallic, natural orsynthetic material composed of large or small molecules formed of manyrepeating, linked units. A co-polymer is a mixed polymer, the product ofpolymerization of two or more substances at the same time. A blockco-polymer is a co-polymer in which the like monomer units occur inrelatively long, alternate sequences on a chain. Block co-polymers areprepared by taking advantage of special chemical or kinetic situations.The ability to synthesize a wide variety of these materials is morerestricted than it is in the synthesis of random, alternating, orrandom-alternating-type co-polymers. Nevertheless, ingenious techniqueshave been devised to synthesize block co-polymers, some of widerapplicability and importance than others. Two of the more importanttechniques are the anionic living polymer process and the free radicalprocess.

The routes leading to block co-polymers generally involve the reactionof fresh monomer(s) with a previously prepared parent homo-polymer orco-polymer. The various sequences may be either homo-polymer orco-polymer in nature. In the special case of generating blockco-polymers via the anionic living polymer technique, the parenthomo-polymer is still active. For the most part, block co-polymerizationinvolves initiating polymerization reactions through active sites boundon the parent polymer molecule. Block co-polymerization involvesterminal active sites. Polymerization is usually conducted in a mixtureof the parent polymer, the monomer(s) to be grown on the parent polymer,and fresh initiator.

If polymerization is conducted in a mixture of monomer, initiator, andpolymer, a mixture of products may result: (1) homo-polymer of freshmonomer; (2) homo-polymer of the parent molecules that did not take partin the co-polymerization; (3) cross-links between the branchedstructures; and (4) the desired co-polymer. For any system having thepotential to produce a high yield of the desired product, reactionconditions must be controlled so as to suppress those leading to thefirst three types of products and to enhance those leading to thedesired co-polymer. In some instances, it may be possible to applyseparation processes to obtain a pure product.

One aspect of the present invention is to use polymers to form acombination co-polymer insulator and organic semiconductor (includingcarbon-based nanotubes). Another aspect is to use the combinationinsulator and organic semiconductor structure so formed to manufacturesemiconductor devices such as thin-film transistors. Co-polymerscomprised of chemically distinct polymers linked together canself-assemble into well-ordered structures such as lamellas, cylinders,dots, and the like as described by M. Lazzari and M. López-Quintela,“Block Copolymers as a Tool for Nanomaterial Fabrication,” 15 AdvancedMaterials, No. 19, pages 1583–94 (Oct. 2, 2003) (incorporated in thisdocument by reference). By using the self-assembly of co-polymerscomprised of an insulator and an organic semiconductor, the presentinvention improves the formation of layers of semiconductor devices andimproves the structure of transistors.

A. Self-Assembling Co-Polymer Combination Insulator and OrganicSemiconductor Structures

Referring now to the drawing, in which like reference numbers refer tolike elements throughout the various figures that comprise the drawing,FIGS. 3A (cross-section) and 3B (top view) show a co-polymer lamellastructure 30 formed according to the present invention. FIGS. 3A and 3Bshow thin-film co-polymer lamella structure 30 self-assembled frompolymers comprised of the insulator 1 and the organic semiconductor 2.As best illustrated in FIG. 3A, insulator 1 and organic semiconductor 2of lamella structure 30 are layered in parallel (i.e., the layers arehorizontally oriented) with insulator 1 on the top and organicsemiconductor 2 on the bottom.

By forming lamella structure 30 on a substrate 3, a thin-film transistorcan be manufactured using a relatively simple process. In addition, theprocess minimizes the risk of forming an imperfect or contaminatedinterface between insulator 1 and organic semiconductor 2. Statedalternatively, the interface between insulator 1 and organicsemiconductor 2 is substantially free of contamination. Substrate 3 canbe various shapes including, but not necessarily limited to, a flatplate, a curved plate, a wire, a sphere, or cubes.

The formation of co-polymer lamella structure 30 from polymers is donewhen the polymers are heated above the glass transition temperature(T_(g)). As is well-known in the art, the properties of polymermaterials vary with temperature. At sufficiently low temperatures,amorphous polymers are hard and glass-like, having a relatively highmechanical strength. This state is maintained as the temperature israised until a critical temperature region is attained. Within thisregion, the polymer changes from a hard, glass-like, inflexible materialto a softer, rubbery, flexible material. This drastic transition inmechanical properties is called the glass transition, and the criticaltemperature is called the glass transition temperature.

Once heated above T_(g), the insulator polymer material and the organicsemiconductor polymer material go into phase segregation. When theco-polymer combination is cooled down from T_(g), the lamella structureremains and forms the two-layer structure shown in FIG. 3A. Themolecular self-assembly of the block co-polymer produces, in a simpleprocess, a useful lamella structure 30 without any direct humanintervention.

Lamella structure 30 of FIGS. 3A and 3B can be used, for example, toform an improved bottom contact thin-film transistor structure similarto the conventional structure illustrated in FIG. 1. FIG. 1 shows across-section of bottom contact structure 10. Upon incorporation oflamella structure 30 into bottom contact structure 10, organicsemiconductor 2 contacts each of substrate 3, source electrode 4, anddrain electrode 5.

Of course, as would be recognized by an artisan, insulator 1 and organicsemiconductor 2 of lamella structure 30 may be layered in parallel, orhorizontally oriented, with insulator 1 on the bottom and organicsemiconductor 2 on the top. With the order of the layers reversedrelative to the order shown in FIG. 3A, lamella structure 30 can be usedto form an improved top contact thin-film transistor structure similarto the conventional structure illustrated in FIG. 2. FIG. 2 shows across-section of top contact structure 20. Upon incorporation ofreversed lamella structure 30 into top contact structure 20, insulator 1contacts each of substrate 3 and gate electrode 6.

The process of forming lamella structure 30 can be easily controlled toyield either bottom contact structure 10 of FIG. 1 (in whichsemiconductor 2 contacts substrate 3) or top contact structure 20 ofFIG. 2 (in which insulator 1 contacts substrate 3). One process controluses the chemical affinity between the surface of substrate 3, perhapsincluding electrodes 4 and 5, and either insulator 1 or organicsemiconductor 2; the chemical affinity can be determined by materialproperties or by an altered surface treatment. Another process controluses the different densities of the two polymers that form insulator 1and organic semiconductor 2, respectively: a denser polymer tends tosink in solution so that the lighter polymer tends to form on top of thedenser polymer.

FIG. 4A (cross-section) and 4B (top view) show a co-polymer cylinderstructure 40 formed according to the present invention. FIGS. 4A and 4Bshow thin-film co-polymer cylinder structure 40 self-assembled frompolymers comprised of the insulator 1 and the organic semiconductor 2.As best illustrated in FIG. 4A, insulator 1 and organic semiconductor 2of cylinder structure 40 are layered in parallel, or horizontallyoriented, with cylindrical structures of organic semiconductor 2surrounded in a matrix of insulator 1.

Parallel cylinder structure 40 can be formed using processes as outlinedabove, in connection with lamella structure 30, and as described in moredetail by authors M. Lazzari and M. López-Quintela. As the authors note,polymers represent ideal nanoscale tools given their intrinsicdimensions, ease of synthesis and processing, strict control ofarchitecture, chemical functionality, and unique mesophase separationboth in bulk and in solution—particularly in the case of blockco-polymers. Parallel cylinder structure 40 of FIGS. 4A and 4B can beused, for example, to form an improved multi-gate thin-film transistoras shown in FIGS. 10A–10E and discussed in detail below.

FIG. 5A (cross-section) and 5B (top view) show a co-polymer cylinderstructure 50 formed according to the present invention. FIGS. 5A and 5Bshow thin-film co-polymer cylinder structure 50 self-assembled frompolymers comprised of the insulator 1 and the organic semiconductor 2.As best illustrated in FIG. 5A, which is a cross-section taken along theline 5A—5A of FIG. 5B, insulator 1 and organic semiconductor 2 ofcylinder structure 50 are vertically layered, with cylindricalstructures of organic semiconductor 2 surrounded in a matrix ofinsulator 1.

Vertical cylinder structure 50 can be formed using processes as outlinedabove, in connection with lamella structure 30, and as described in moredetail by authors M. Lazzari and M. López-Quintela. Upon formation,vertical cylinder structure 50 can be incorporated into a thin-filmtransistor. Vertical cylinder structure 50 of FIGS. 5A and 5B can beused, for example, to form an improved multi-gate thin-film transistoras shown in FIGS. 11A–11F and discussed in detail below.

FIGS. 6A (cross-section) and 6B (top view) show a co-polymer lamellastructure 60 formed according to the present invention. FIGS. 6A and 6Bshow thin-film co-polymer lamella structure 60 self-assembled frompolymers comprised of the insulator 1 and the organic semiconductor 2.As best illustrated in FIG. 6A, insulator 1 and organic semiconductor 2of lamella structure 30 are layered in a vertical orientation, withalternating lamellae of insulator 1 and semiconductor 2.

Vertical lamella structure 60 can be formed using processes as outlinedabove, in connection with lamella structure 30, and as described in moredetail by authors M. Lazzari and M. López-Quintela. Upon formation,vertical lamella structure 60 can be incorporated into a thin-filmtransistor. Vertical lamella structure 60 of FIGS. 6A and 6B can beused, for example, to form an improved multi-gate thin-film transistoras shown in FIGS. 12A–12F and discussed in detail below.

B. General Multi-Gate Semiconductor Transistors

As discussed above, multi-gate semiconductor structures offer severaladvantages in comparison to single-gate structures. Therefore, theinventors recognized the desirability of using the self-assemblingco-polymer combination insulator and organic semiconductor structures ofthe present invention to manufacture multi-gate semiconductorstructures. FIGS. 7A (cross-section) and 7B (side view) illustrate asingle-gate transistor structure for comparison purposes. As bestillustrated in FIG. 7A, which is a cross-section taken along the line7A—7A of FIG. 7B, cylindrical organic semiconductor 2 is surrounded in amatrix of insulator 1. The single gate electrode 6 is formed on top ofinsulator 1 (although gate electrode 6 could be formed on any portion ofinsulator 1, as dictated by the application). The source electrode 4 andthe drain electrode 5 are each formed at opposite ends of cylindricalorganic semiconductor 2.

FIGS. 8A (cross-section) and 8B (side view) illustrate a dual-gatetransistor structure. Again, as best illustrated in FIG. 8A, which is across-section taken along the line 8A—8A of FIG. 8B, cylindrical organicsemiconductor 2 is surrounded in a matrix of insulator 1. Like thesingle-gate transistor structure of FIGS. 7A and 7B, the sourceelectrode 4 and the drain electrode 5 are each formed at opposite endsof cylindrical organic semiconductor 2. Unlike the single-gatetransistor structure of FIGS. 7A and 7B, however, the dual-gatetransistor structure of FIGS. 8A and 8B has a first gate electrode 6 aformed adjacent a first portion of insulator 1 and a second gateelectrode 6 b formed adjacent a second portion of insulator 1.

FIGS. 9A (cross-section) and 9B (side view) illustrate a tri-gatetransistor structure. Again, as best illustrated in FIG. 9A, which is across-section taken along the line 9A—9A of FIG. 9B, cylindrical organicsemiconductor 2 is surrounded in a matrix of insulator 1. Like thesingle and dual-gate transistor structures discussed above, the sourceelectrode 4 and the drain electrode 5 are each formed at opposite endsof cylindrical organic semiconductor 2. Unlike the prior structures,however, the tri-gate transistor structure of FIGS. 9A and 9B has afirst gate electrode 6 a formed adjacent a first portion (e.g., the top)of insulator 1 and two additional gate electrodes 6 c formed adjacentother portions (e.g., either side) of insulator 1.

Although not illustrated, a transistor structure having four gateelectrodes is also possible. A first gate electrode is formed on top ofthe insulator 1. A second gate electrode is formed on the bottom of theinsulator 1. And two additional gate electrodes are formed on eitherside of insulator 1.

C. Specific Multi-Gate Semiconductor Transistors

Described in detail below are several embodiments of the processes thatmay be used to form multi-gate thin-film transistors, using the variousself-assembling co-polymer combination insulator and organicsemiconductor structures described above, according to the presentinvention. Turning first to the parallel cylinder structure 40illustrated in FIGS. 4A and 4B, such structure 40 is incorporated into amulti-gate thin-film transistor structure via the process illustrated inFIGS. 10A–10E. The process begins by providing a substrate 3 as shown inFIG. 10A.

Next, as shown in FIG. 10B, the polymers are deposited on substrate 3and cylinders of the organic semiconductor 2 are self-assembled in thedirection parallel to the thin film within the matrix of the insulator1. Compare FIG. 10B with the self-assembling co-polymer combinationinsulator and organic semiconductor structure of FIG. 4A. The nextprocessing step is to separate the individual cylinders by removingparts of insulator 1 between the cylinders of organic semiconductor 2.The structure resulting after this step is shown in FIG. 10C. Then thegate electrodes 6 are formed around the insulator 1, as illustrated inFIG. 10D. Gate electrodes 6 may be separated for applications in whichindividual control is necessary. Finally, the source electrode 4 and thedrain electrode 5 are formed at the ends of organic semiconductors 2, asshown in FIG. 10E.

In another embodiment, the process steps used to form a multi-gatetransistor are illustrated sequentially in FIGS. 11A–11E. These processsteps incorporate the vertical cylinder structure 50 illustrated inFIGS. 5A and 5B. The process begins by providing a substrate 3 as shownin FIG. 11A.

Next, as shown in FIG. 11B, the polymers are deposited on substrate 3,which has patterned source (or drain) electrodes, and cylinders of theorganic semiconductor 2 are self-assembled in the directionperpendicular to the thin film within the matrix of the insulator 1preferentially on the electrodes. Compare FIG. 11B with theself-assembling co-polymer combination insulator and organicsemiconductor structure of FIG. 5A. The location preference may becontrolled in various ways, such as preferable affinity between theelectrodes and organic semiconductors 2 which may naturally occur; bysurface treatment of the electrodes; by a stress field induced throughgeometrical differences; by an electrical field applied via theelectrodes; by applying a magnetic field; or by any other suitablemechanism as would known to an artisan.

The next processing step is to separate the individual cylinders byremoving parts of insulator 1 between the cylinders of organicsemiconductor 2. The structure resulting after this step is shown inFIG. 11C. Then the gate electrodes 6 are formed around the insulator 1,as illustrated in FIG. 11D. Gate electrodes 6 may be separated forapplications in which individual control is necessary. Finally, thesource electrode 4 and the drain electrode 5 are formed at the ends oforganic semiconductors 2, as shown in FIG. 11E. FIG. 11F is a top viewof the final structure illustrated in cross-section by FIG. 11E.

In yet another embodiment, the process steps used to form a multi-gatetransistor are illustrated sequentially in FIGS. 12A–12E. These processsteps incorporate the vertical lamella structure 60 illustrated in FIGS.6A and 6B. The process begins by providing a substrate 3 as shown inFIG. 12A.

Next, as shown in FIG. 12B, the polymers are deposited on substrate 3and the vertically self-assembled lamella structure is formed. Thestructure includes the insulator 1 and the organic semiconductor 2layered in a vertical orientation, with alternating lamellae ofinsulator 1 and semiconductor 2. Compare FIG. 12B with theself-assembling co-polymer combination insulator and organicsemiconductor structure of FIG. 6A.

The next processing step is to separate the individual organicsemiconductors 2, which are sandwiched by insulators 1, by removingparts of insulator 1 between organic semiconductors 2. The structureresulting after this step is shown in FIG. 12C. Then the gate electrodes6 are formed around the insulator 1, as illustrated in FIG. 12D. Gateelectrodes 6 may be separated for applications in which individualcontrol is necessary. Finally, the source electrode 4 and the drainelectrode 5 are formed at the ends of organic semiconductors 2, as shownin FIG. 12E. FIG. 12F is a top view of the final structure illustratedin cross-section by FIG. 12E.

By self-assembling polymers of the insulator and organic semiconductorinto a co-polymer structure, both layers in a thin-film transistor canbe formed simultaneously. Further, the interface between the insulatorand semiconductor is substantially free of imperfection orcontamination. Still further, the process steps required to produce athin-film transistor are reduced and simplified relative to conventionalmanufacturing processes. Finally, many of the obstacles previouslyencountered by attempts to fabricate multi-gate thin-film transistorsare overcome by using self-assembling co-polymers according to thepresent invention.

As mentioned above, among the organic semiconductors suitable for use inthe present invention are carbon nanotubes. Although the presentinvention encompasses both multi-walled and single-walled carbonnanotubes, the focus of the following discussion is on the latter.Single-walled nanotubes or SWNTs (sometimes called “buckytubes”) arehollow molecules of pure carbon linked together in an hexagonally bondednetwork to form a hollow polymer cylinder. The tube is seamless, witheither open or capped ends, and is free of property-degrading flaws inthe nanotube structure. The diameter of an individual SWNT is 0.7 to 2nm, typically about 1.0 nm, which is about 100,000 times thinner than ahuman hair, about half the diameter of DNA, and about 1/10,000^(th) thediameter of graphite fibers. Individual tubes are about 100–1,000 nm inlength, hundreds of times their diameters, giving SWNTs a very highaspect ratio. Specifically, the aspect ratio of a SWNT is around100–1,000, compared with about 1 for carbon black particles. The specialnature of carbon combines with the molecular structure of the SWNT togive SWNTs exceptionally high material properties such as electrical andthermal conductivity, strength, stiffness, and toughness.

SWNTs can be reacted and manipulated using the rich chemistry of carbon.Thus, a SWNT gives the user an opportunity to modify the structure andto optimize solubility and dispersion. The material characteristics ofthe SWNT give the SWNT potential in numerous applications, including useas filler in thermoplastics and thermosets. In fact, SWNTs naturallyform a morphology that is ideal for conductive filler applications.SWNTs self-assemble into “ropes” of tens to hundreds of aligned tubes,running side by side, branching and recombining. When examined byelectron microscopy, it is exceedingly difficult to find the end of anyof these ropes. Thus, ropes form naturally occurring, long, conductivepathways that can be exploited in making electrically conductive filledcomposites.

Additional information about SWNTs can be obtained from CarbonNanotechnologies, Incorporated of Houston, Tex. (www.cnanotech.com).More generally, the United States government provides information aspart of its National Nanotechnology Initiative (“NNI”). A discussion ofthe emerging field of nanotechnology, the science of manipulatingmaterials on an atomic or molecular scale, can be found at www.nano.gov.

Although the invention is illustrated and described above with referenceto specific embodiments, the invention is not intended to be limited tothe details shown. Rather, various modifications may be made in thedetails within the scope and range of equivalents of the claims andwithout departing from the invention.

1. A process of manufacturing a thin-film organic semiconductor device,the process comprising: (a) providing a substrate; (b) applying to thesubstrate an insulator layer formed of a first polymer and an organicsemiconductor layer formed of a second polymer, wherein the polymersself-assemble into a well-ordered co-polymer structure with thesemiconductor layer positioned adjacent the insulator layer; and (c)removing parts of the insulator between the organic semiconductor layer,thereby separating the layers of organic semiconductor.
 2. The processof claim 1, wherein the co-polymer is a block co-polymer.
 3. The processof claim 1, wherein the organic semiconductor layer comprisescarbon-based nanotubes.
 4. The process of claim 1, wherein an interfacebetween the insulator layer and the organic semiconductor layer issubstantially free of contamination.
 5. The process of claim 1, furthercomprising the step of forming at least one gate electrode on an exposedsurface of the insulator layer.
 6. The process of claim 5, furthercomprising the step of forming a source electrode and a drain electrodeat the ends of the organic semiconductor layer.
 7. The process of claim1, further comprising the step of forming at least two gate electrodeson an exposed surface of the insulator layer.
 8. The process of claim 7,further comprising the step of separating the at least two gateelectrodes.